Vehicles with liquid cooled engines generally mount the engine cooling heat exchanger (radiator) at the front of the engine compartment, just behind the bumper and grille, so as to take advantage of the ram air effect at higher vehicle speeds. At lower vehicle speeds, an axially acting engine cooling fan forces air through the radiator. In commercial practice, the fan is generally mounted to a support shroud that both physically secures the fan to the vehicle, and which also surrounds the fan to confine and direct the air efficiently through the radiator. While radiators are typically planar, rectangular structures, the fans are invariably circular, with blades extending radially from a central hub. The inefficiency resulting from this inevitable radiator-fan shape mismatch is reduced by the air ducting action of the shroud, and can be further reduced by using two, side by side fans. The air drawn through the radiator is significantly heated above ambient temperature, typically as much as 80 degrees F above ambient temperature.
Vehicles that also have an air conditioning system generally mount a condenser in front of the radiator. Since condensers operate at significantly lower temperatures than the radiator, it would not be practical to mount them behind the radiator. Therefore, air that is forced through the radiator first flows through the condenser, and is raised in temperature far less, only on the order of 10 degrees F above ambient.
Fan and fan shroud location, in actual commercial practice, is almost invariably behind the radiator, so as to pull air through both the condenser and radiator. The fan and fan shroud materials must obviously be designed to withstand the higher, downstream radiator air temperatures. An obviously cooler location would be upstream, in front of both the condenser and radiator, but this location is invariably rejected due to vulnerability to damage, and, in the case of engine belt driven fans, inaccessibility to the belt. It has also been proposed to place the engine cooling fan in the one remaining possible location, which is the intermediate location between the condenser and radiator, a location that became feasible with the more recent advent of electrically driven cooling fans. This location of the cooling fan is generally touted only as a space saving measure, without any particular recognition of, or use for, the cooler condition of the air found in the intermediate fan location.
As an example of intermediate fan location, U.S. Pat. No. 4,510,991 discloses a fan mounted to the drive shaft of a motor that is mounted to or through the condenser, thereby putting the fan itself between the condenser and radiator. Various novel circular condenser designs better matched to the shape of the fan are disclosed, but there is no particular recognition that the location of the fan is beneficial in terms of cooler air. More recent U.S. Pat. No. 5,771,961 proposes similar designs, also fixing the drive motors to the condenser face, and potentially even placing the fan itself within a very large and ill defined through hole in the condenser. Doing this would remove so much condenser volume and area as to render it essentially unworkable. The disclosure also speaks in terms of eliminating the fan shroud, although air confinement rings surrounding the fan are disclosed, which would be necessary to proper fan air ducting and routing. As a practical matter, any proposal that required a drastic redesign of the standard condenser would not find any significant commercial use.
A more recent trend in new vehicle design is the recognition that many components located within the increasingly crowded and small engine compartments need, or could at least benefit from, forced cooling. Examples include batteries, alternators, and various heat producing electrical components. Two recent co assigned US patents propose forced air, underhood component cooling systems. U.S. Pat. No. 5,671,802 discloses a hose and box system that houses a heat producing component and routes ram air from the front of the vehicle through the box. This utilizes ambient air temperature for cooling, but, of course, can provide no forced cooling air when the vehicle is idling. U.S. Pat. No. 5,775,450 provides essentially the converse in terms of benefit and shortcomings. A scoop behind the fan (which fan is behind the radiator) diverts some of the fan forced air up and over the alternator, cooling it whenever the fan is running, but using air that has been heated by the radiator significantly above ambient temperature. There are components for which each system will work perfectly well, that is, those that do not need a continual stream of air, or which can benefit from cooling even by warmer air. However, there are underhood components that would potentially benefit both from a continual supply of forced cooling air, especially if the air were cooler than the air that has already passed through the radiator.
To summarize, all of the inherent space saving advantages of the intermediate cooling fan location are retained, with no change in the basic heat exchanger design, while an improved, forced air component cooling is achieved with minimal additional structure and cost.